This application relates to wireless communication systems and techniques.
Wireless communication systems use electromagnetic waves to communicate with wireless communication devices located within cells of coverage areas of the systems. A radio spectral range or band designated or allocated for a wireless communication service or a particular class of wireless services may be divided into different radio carrier frequencies for generating different communication frequency channels. For a given wireless system, the communication capacity increases as the number of the communication frequency channels increases. Two different frequency channels, when placed too close to each other in frequency, can interfere or cross talk with each other to create noise and thus reduce the signal-to-noise ratio. One technique to reduce the minimum frequency spacing between two adjacent channels is to generate different channels within a given band by using the orthogonal frequency division multiplexing (OFDM) to generate channel spectral profiles that are orthogonal to one another without interference when different channels are centered at selected equally-spaced frequencies. Under the OFDM, the frequency spacing can be smaller than the minimum spacing in conventional frequency channels and hence increase the number of channels within a given band. The existing and developing specifications under IEEE 806.16x standards support wireless communications under OFDM and orthogonal frequency division multiple access (OFDMA). The draft for IEEE 806.16d published in January 2004 provides technical specifications for OFDM and OFDMA wireless systems.
In OFDM and OFDMA systems, it is desirable to control the transmitting power levels at different frequencies in order to achieve desired system operations, e.g., maintaining a certain level of the system performance such as the quality of service (QoS).